Capsule endoscope

ABSTRACT

A capsule endoscope is disclosed that includes means for illuminating an object, means for imaging the object, and a transparent cover having a center of curvature. The transparent cover covers the illumination means and the imaging means, and the imaging means includes an objective optical system and an image detecting element. The illumination means is positioned relative to the image detecting element, as viewed axially from the object side of the capsule endoscope, so that an area that is symmetrically positioned about the optical axis of the objective optical system from a light emitting area of the illumination means overlaps an area of the image detecting element, but does not overlap any areas of the image detecting element that are used for image detection.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of foreign priority from JapanesePatent Application No. 2002-064016, filed Mar. 8, 2002, the contents ofwhich are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

Endoscopes have recently come into extensive use in the medical andindustrial fields. Recent medical endoscopes do not have an insertionmember and there is no longer an insertion process. These are medicalendoscopes are encapsulated within a capsule, which a patient canswallow. This eliminates the pain associated with insertion of prior artendoscopes that have an insertion member. Examples of capsule endoscopesinclude, for instance, those disclosed in the Japanese Laid-Open PatentApplication 2001-91860 and the patent publication PCT WO 00/76 391 A1.

The prior art capsule endoscope disclosed in Japanese Laid-Open PatentApplication 2001-91860 is provided with an objective lens and anillumination means consisting of light emitting diodes symmetricallylocated in relation to the objective lens within a nearly semi-sphericaltransparent cover. Part of the object is illuminated by the lightemitting diodes and imaged by the objective lens onto an image sensorfor observation. The prior art capsule endoscope disclosed in patentpublication PCT WO 00/76 391 A1 includes a single, oval dome, opticalwindow. An illumination element and a receiving element are positionedabove or in contact with the focal curve plane of the oval dome. Pluralillumination elements are positioned on the focal curve so that lightfrom the illumination elements returns to some other point on the focalcurve when a portion of the illumination light is reflected by the innerand outer surfaces of the window. Therefore, the receiving element ispositioned somewhere other than on the focal curve in order to preventlight that is reflected at the interfaces of the oval dome surface fromentering the receiving element, thereby preventing flare and ghostingthat adversely affect the proper detecting of images.

The prior art capsule endoscope disclosed in Japanese Laid-Open PatentApplication 2001-91860 does not describe a means to prevent or reduceflare and ghosting caused by a portion of the illumination light fromthe illumination means entering the objective lens after it has beenreflected at air interfaces of the transparent cover. The prior artcapsule endoscope disclosed in patent publication PCT WO 00/76 391 A1uses an oval dome, transparent cover for the illumination andobservation window, which is more costly to produce than asemi-spherical transparent cover. Furthermore, plural illuminationelements are positioned on the focal curve. Since each element should beadjusted in position, this design requires additional labor.

When the illumination elements are light emitting elements (LEDs), theilluminating elements have a non-insignificant size. Therefore, in orderto position the LEDs on the focal curve, the focal curve must besufficient in length to accommodate the area in which the LEDs are to bepositioned. This causes the size of the oval dome to become larger,which disadvantageously requires that the capsule be larger. However,increasing the size of the capsule is undesirable because it becomesdifficult, even painful, to swallow such an encapsulated endoscope.Thus, the advantage of using a capsule endoscope is lost. Accordingly,the arrangement of the illumination means and the image detectingelement within a capsule must be designed in a manner whereby thecapsule can be made as compact as possible.

BRIEF SUMMARY OF THE INVENTION

The present invention relates to a capsule endoscope that is swallowedin order to examine interior regions of a living body. Moreparticularly, the present invention provides a small-sized capsuleendoscope having a transparent cover that is easy and inexpensive tomanufacture, and which makes it difficult for undesirable light from theillumination means to enter the objective optical system.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will become more fully understood from the detaileddescription given below and the accompanying drawings, which are givenby way of illustration only and thus are not limitative of the presentinvention, wherein:

FIGS. 1(A) and 1(B) shows a capsule endoscope system which uses acapsule endoscope according to Embodiment 1 of the present invention;

FIG. 2(A) shows a sectional view of the internal structure of a capsuleendoscope, and FIG. 2(B) shows the positional relationship between theimage detecting means and the illumination means, when viewing thecapsule endoscope axially from the object side, according to Embodiment1 of the invention;

FIG. 3 is an enlarged view of the objective optical system and the imagesurface of a CMOS image detecting element according to the presentinvention;

FIGS. 4(A) and 4(B) show the effects of an objective optical system thatuses a semi-spherical window, with FIG. 4(A) illustrating the situationof the illuminating light being positioned at the center of curvature ofthe semi-spherical transparent cover, and with FIG. 4(B) illustratingthe situation of the illuminating light being positioned somewhere else;

FIG. 5 is a cross-sectional view showing the structure of a capsuleendoscope according to Embodiment 2 of the present invention;

FIG. 6 is an illustration to explain details concerning the operation ofthe transparent cover;

FIG. 7 is a cross-sectional view showing the structure of a capsuleendoscope according to a first possible modification to Embodiment 2 ofthe present invention;

FIG. 8 is a cross-sectional view showing the structure of a capsuleendoscope according to a second possible modification to Embodiment 2 ofthe present invention;

FIG. 9 is a cross-sectional view showing the structure of a capsuleendoscope according to a third possible modification to Embodiment 2 ofthe present invention;

FIGS. 10(A) and 10(B) relate to Embodiment 3 of the present invention,with FIG. 10(A) being a cross-sectional view, and FIG. 10(B) showing thepositional relationship between the illumination means and the imagedetecting element when viewing the capsule endoscope axially from theobject side;

FIGS. 11(A)-11(D) relate to Embodiment 4 of the present invention, withFIG. 11(A) being a cross-sectional view, with FIG. 11(B) showing the ONstate, with FIG. 11(C) showing the positional relationship between theillumination means and the image detecting element when viewing thecapsule endoscope axially from the object side, and with FIG. 11(D)showing a possible modification to the positional relationship shown inFIG. 11(C);

FIGS. 12(A)-12(C) relate to Embodiment 5 of the present invention, withFIG. 12(A) being a cross-sectional view of the tip portion of thecapsule endoscope, with FIG. 12(B) showing the positional relationshipbetween the illumination means and the image detecting element whenviewing the capsule endoscope axially from the object side, and withFIG. 12(C) showing a first possible modification to the positionalrelationship shown in FIG. 12(B);

FIGS. 13(A) and 13(B) relate to a second possible modification toEmbodiment 5 wherein, instead of using a single lens for imaging, leftand right imaging systems that are capable of providing images havingdifferent parallax for 3-D viewing are positioned within the capsule,with FIG. 13(A) being a cross-sectional view showing a construction ofthe main components of the tip portion of a capsule endoscope thatincludes a plurality of objective optical systems, and with FIG. 13(B)showing the positional relationship between the imaging means and theillumination means when viewing the capsule endoscope axially from theobject side;

FIGS. 14(A) and 14(B) relate to a third possible modification toEmbodiment 5, with FIG. 14(A) showing a cross-sectional view of theconstruction of the main components of the tip portion of a capsuleendoscope comprising a plurality of objective optical systems, and withFIG. 14(B) showing the positional relationship between the imaging meansand the illumination means when viewing the capsule endoscope axiallyfrom the object side;

FIG. 15 is a cross-sectional view illustrating a capsule endoscope ofthe present invention moving within a lumen-shaped part of a livingbody; and

FIGS. 16(A) and 16(B) show two different light flux distributions, withFIG. 16(A) being the light flux distribution of a beam emitted from anLED such that the half-beam angle, as measured at the 50% of peakintensity points, is 25°, and with FIG. 16(B) being the light fluxdistribution of a beam emitted from an LED having a diffusion means suchthat the half-beam angle, as measured at the 50% of peak intensitypoints is larger, in this case 35°.

DETAILED DESCRIPTION

The capsule endoscope of the present invention employs a transparent,dome-shaped cover, the inner surface of which has a center of curvature.Within the transparent cover there are provided a lighting means forilluminating an object outside the transparent cover and an imagingmeans which includes an objective optical system and an image detectingelement that captures image data of an image formed by the objectiveoptical system. The objective optical system may be arranged so that itsoptical axis lies on the center of curvature of the inner surface of thetransparent dome.

When observing the internal wall of a lumen of a living body, the viewfield of interest is often at the periphery of the visual field. Atransparent cover that is formed of a curved surface is installed infront of the imaging means, and the transparent cover is sealed to thecapsule body. In such a case, the lumen-shaped internal part of interestat the periphery of the visual field is so near to the illuminationmeans that over-exposure often occurs at the periphery of the visualfield. More specifically, the capsule endoscope is constructed suchthat, when viewing the capsule endoscope from the object side, thepositional relationship between the illumination means and the imagingmeans is determined so that an area that is symmetrical about theoptical axis to the illumination means overlaps onto areas other thanimage-capturing areas of the image detecting element. In one case, apart of an image detecting area of the image detecting device is coveredby an opaque member and the area that is symmetrical about the opticalaxis to the illumination means overlaps the covered area. In anothercase, a part of the image detecting area of the image detecting elementis electrically masked so as to make the masked area inoperative and thearea that is symmetrical about the optical axis to the illuminationmeans overlaps the electrically masked area. Here, the word“inoperative” includes either that the pixels within an electricallymasked area produce no electrical signal, or that they produceelectrical signals which are not used to construct the image to beobserved. In still another case, the area that is symmetrical about theoptical axis to the illumination means overlaps the area outside theimage detecting area. In either case, the area that is symmetrical aboutthe optical axis to the illumination means overlaps an area of the imagedetecting element but does not overlap any area of the image detectingelement that is used for picture image detection. Therefore, even whenan illuminating beam is reflected by the internal surface of thetransparent cover, such unwanted light will not contribute to thecaptured image, since it will not be incident onto active areas of theimage detecting device.

FIG. 15 is a cross-sectional view illustrating the state of a capsuleendoscope at the time of performing observations while moving within asmall-diameter, lumen-shaped part within a living body. About 80% of thelength of the human digestive tract (i.e., the usual observation pathfor a capsule endoscope) is within the intestine, which has a smalldiameter. The lumen-shaped internal part 90 has a portion 91 that liesimmediately adjacent to the transparent window, and this portion (whichis of primary interest) tends to become over-exposed by the illuminationmeans 92. In a capsule endoscope having a transparent cover with aradius of curvature of about 5 mm, the over-exposed portion 91 of theobject lies in a range that is centered about 3 mm from the illuminationmeans 92. In this FIG. 93 is the objective optical system, 94 is theimage detecting element, and 100 is the image plane.

An LED is usually used as the illumination means. With Such anillumination means, there is a region that contributes particularlystrongly to the illumination at the irradiated plane. Generallyspeaking, an LED's light flux output has a Gaussian distribution, withabout 75% of the total light that is output being concentrated within anangular range, as measured from the optical axis of the LED, where theintensity ratio exceeds 0.5. This light strongly influences theillumination distribution at the irradiated plane. As shown in FIG.16(A), light emitted from an LED has a flux distribution with a strongdirectivity, with the beam width (as measured on the X-axis) where thenormalized intensity ratio (measured on the Y-axis) exceeds 0.5 beingapproximately 25°. Light rays emitted outside this beam width do nothave a large effect on the illumination distribution at the irradiatedplane. When using an LED having an improved flux distribution propertyas shown in FIG. 16(B), wherein a diffusion function is provided by alight diffuser positioned immediately in front of the LED, the beamwidth (as measured on the X-axis) where the normalized intensity ratio(measured on the Y-axis) exceeds 0.5 is about 35°. The latter case ispreferred for use as the illumination means of a capsule endoscope. AtSuch time, if the light emitting plane of the LED is a circle having theradius r, the radius r is enlarged by a factor of approximately 2 to 3.5when projected to a plane 3 mm ahead of the light emitting plane of theLED.

The image-formation relationship at the time of passing through anobjective optical system 93 will now be described. An over-exposedportion 91 is an area that extends outside the visual field angle θ, andin this region photographic objects are reduced in size and form animage at a ‘symmetrical area’ on the image plane 100 that is on theopposite side of the optical axis of the objective optical system 93.The magnification of the objective optical system of a capsule endoscopefor an object that is adjacent the transparent cover is in the rangefrom about 0.25 to 0.5. On the other hand, the range where the objectiveoptical system 93 is able to actually form an image on the image planewill be larger than the visual field angle θ as shown in FIG. 15.Accordingly, in the objective optical system of a capsule endoscope, thearrangement relationship between the objective optical system and theimage detecting element is set so that an image-forming area from theexcessive luminous flux outside the visual field angle θ is incident onan area of the image detecting element that is not used for imagedetection. Or, alternatively to such an arrangement, the range of thevisual field angle θ may instead be determined by electrically maskingthe image-formation area outside the visual field angle θ at the time ofpicture image processing.

Therefore, the positional relationship between the illumination meansand the imaging means when these components lie on opposite sides of theoptical axis as viewed from the front of the capsule endoscope must bedetermined appropriately for a small-scale capsule endoscope in order toprovide a visual field as large as possible and to provide a properbrightness so that over-exposure of an object within the visual fielddoes not occur.

As described above, when using an LED with a light diffuser as theillumination means, the light emitting area of the LED is enlargedapproximately 2 to 3.5 times when the emitted light is projected to aplane about 3 mm in front of the LED, and an object at this distance isthen imaged by the objective optical system onto the image plane. Thelight emitting plane of the diffuser is imaged by the objective opticalsystem with a magnification of approximately 0.9 to 1.0 because themagnification of the objective optical system in relation to an adjacentobject is approximately 0.25 to 0.5. The position of the image issymmetrically located about the optical axis opposite the LED. Thisimplies that an area on the image-detecting surface that is symmetricabout the optical axis to the light emitting area of the LED withdiffuser, when viewing the capsule endoscope axially from the objectside, nearly matches the light emitting area of the LED with diffuser.

From the above description, if an area at the image plane that overlapswith an area that is symmetrical to the illumination means is made to bean area not used for imaging, the over-exposed portion can be avoidedfrom being made into a picture image. In this manner, the highluminescent intensity of the illumination means can be avoided fromdegrading an image of an object by over-exposing the image.

Further, when the illumination intensity is adjusted based on thebrightness of the image detected by the image detecting element,adjustment error can be avoided as the strong reflected light iseliminated from the image, as described above.

The situation eliminating an over-exposure is explained in detail basedon a typical example of an arrangement and size of the illuminationsource, the objective lens and the image detecting element. Similarsituations exist, in general, in capsule endoscopes, in which anillumination source and an objective optical system are arrangedside-by-side and are covered by a dome-shaped, transparent cover.Therefore the basic idea of the invention can be widely applied tovarious capsule endoscopes. The illumination means 92 and the imagingmeans 94 should preferably be arranged as near to each other as possiblein order to construct a small-sized capsule endoscope. However, if theimage-formation area on the image plane 100 that is symmetrical aboutthe optical axis of the objective optical system 93 to the illuminationmeans 92 is an area used for imaging, an over-exposed object will resultfor objects touching the periphery of the transparent cover, therebyimpeding excellent observation of, for example, the wall of the smallintestine. Accordingly, miniaturization of a capsule endoscope ispreferably achieved by determining the positional relationship betweenthe illumination means 92 and the image detecting means 94 so that anarea that is symmetrically positioned about the optical axis of theobjective optical system to the illumination means 92 overlaps an areawithin the image plane of the image detecting means 94 that is not usedfor imaging. The area not used for imaging is, for instance, a portionknown as ‘optical black’ that is used for detecting the standard levelof optical black in the image plane, and is an area treated with a lightshielding mask, and so forth.

In addition, even when an area that is symmetrical about the opticalaxis to the illumination means is an active image-capturing area of theimage detecting means 94, there is no problem so long as the output fromthis area is ignored during picture image processing (i.e., if this areais ‘electrically masked’).

As described above, a capsule endoscope is provided which has theability to obtain an excellent image having no flare or ghosts and alsoprovides a construction that enables miniaturization. Moreover, evenwhen the shape of the transparent cover is not a spherical shape but isan aspheric shape, a capsule endoscope can be provided which has theability to provide excellent images with little flare and ghosts bydetermining the positional relationship between the illumination meansand the image detecting means so that an area that is symmetrical aboutthe optical axis of the objective optical system to the illuminationmeans overlaps with an area within the image plane of the imagedetecting element that is not used for image detection, and also byproviding a reflection prevention coating on an inside surface of thetransparent cover.

Several embodiments of the present invention will now be described withreference to the drawings.

Embodiment 1

Embodiment 1 will be described with reference to FIGS. 1(A)-4(B). FIGS.1(A) and 1(B) show a capsule endoscope system which uses a capsuleendoscope according to Embodiment 1 of the present invention. FIG. 2(A)is a section view showing the internal structure of the capsuleendoscope. FIG. 2(B) is an illustration showing the positionalrelationship between the image detecting means and the illuminationmeans when viewing the capsule endoscope axially from the object side.FIG. 3 is an enlarged view of the objective optical system. FIGS. 4(A)and 4(B) show the effects of an objective optical system that uses asemi-spherical window, with FIG. 4(A) illustrating the situation of theilluminating light being positioned at the center of curvature of thesemi-spherical transparent cover, and with FIG. 4(B) illustrating thesituation of the illuminating light being positioned somewhere else.

As shown in FIG. 1(A), a capsule endoscope system 1 uses a capsuleendoscope 3 according to Embodiment 1. The capsule endoscope is ingestedby the patient 2 through the mouth and passes through thegastrointestinal tract while wirelessly transmitting image data of theinner walls of the gastrointestinal tract. An antenna unit 4 is providedoutside the patient's body for receiving image data signals from thecapsule endoscope 3, and an external unit 5 is provided for temporarilystoring the images. The external unit 5 includes a built-in hard disk ofa compact flash memory (R) size having a capacity of, for example, 1Gigabyte GB in order to store the image data. Image data stored in theexternal unit 5 can be displayed on a display system 6 (FIG. 1(B))during or after the examination.

As shown in FIG. 1(B), the external unit 5 is detachably connected to apersonal computer 7 that forms the display system 6 via a communicationcable such as a USB cable 8. Images stored in the external unit 5 areuploaded onto the personal computer 7, and then saved in its built-inhard disk and/or processed and displayed on a display 9. The personalcomputer 7 is provided with, for instance, a keyboard 10 for data input.

A USB cable 8 may be provided according to any one of the communicationstandards USB1.0, USB1.1, or USB2. Other serial data communication typescan be used, such as those in accordance with the communicationstandards RS-232C or IEEE 1384. Moreover, parallel data communicationcould also be used.

As shown in FIG. 1(A), the patient 2 swallows the capsule endoscope 3and wears a shielding shirt 11 that includes electrical conductors in amesh arrangement which provide an electromagnetic shielding effect. Theshielding shirt is equipped with an antenna unit 4 that is positionedinside the shielding shirt, (i.e., inside the electrical conductors).The antenna unit 4 receives image data that has been detected andtransmitted by the capsule endoscope 3. The image data is storedtemporarily in an external unit 5 that is connected to the antenna unit4. The external unit 5 is held, for instance, on the patient's belt by adetachable hook.

The external unit has, for instance, a box form and carries a liquidcrystal monitor 13 for displaying images and an operation button 14 onits front cover for controlling operations. The external unit 5 containsa transmission and reception circuit (i.e., a communication circuit), acontrol circuit, an image data display circuit, and an electric powersource.

As shown in FIG. 2(A), the capsule endoscope 3 is formed of acylindrical outer cover 16 having a closed, rounded rear end and an openfront end to which a semi-spherical, transparent cover 17 is affixed andsealed in a watertight manner.

The sealed capsule contains the following components. An objectiveoptical system 23 with its optical axis aligned with a center axis ofthe capsule and faces the semi-spherical, transparent cover 17. Theobjective optical system 23 is fixed to a center barrel of anoctagon-shaped circuit board 21 and to a lens frame 22 that is engagedwith the center barrel of the circuit board 21. A solid-state imagedetecting device, such as a CMOS image detecting element 24 is locatedat the image plane of the objective optical system 23.

As shown in FIG. 2(B), four white LEDs 25 are provided on the frontsurface of the circuit board 21 around the objective optical system 23.Providing the white LEDs 25 at plural points around the objectiveoptical system 23 as an illumination means enables extensive lightdelivery in a short distance so as to provide for excellent qualityobserved images (i.e., captured images).

Further, the miniaturization of a capsule endoscope is devised whilemaintaining a particular positional relationship between a white LED 25and a CMOS image detecting element 24 so that areas that aresymmetrically situated about the optical axis 101 to the white LEDs 25(in this case, these areas correspond to the positions of the LEDs 25)overlap an area that is not used for imaging on the image plane 100 ofthe CMOS image detecting element 24. The white LEDs 25 emit intermittentor flashing light. The image detecting element captures imagessynchronously with the flashing of the white LEDs 25. This allows lowpower consumption and excellent observed images having little blurring,even when there is unexpected motion.

As shown in FIGS. 2(A) and 2(B), the circuit board 21 has a squarerecess on its back surface that accommodates the barrel that supportsthe objective optical system. The CMOS image detecting element 24 ispositioned so that the periphery of its front surface will abut a rearsurface of the circuit board 21 near the periphery of the the recess.Chip members 26 that form an LED driving circuit for driving the whiteLEDs 25 are mounted on the circuit board 21 around the CMOS imagedetecting element 24. On the backside of the CMOS image detectingelement 24, the following components are stacked in the axial directionof the capsule, from front to rear: a driving and processing circuit 27for driving the CMOS image detecting element 24 and processing imagesignals from the CMOS image detecting element 24, a wirelesscommunication circuit 28 for performing high frequency modulation of theimage signals generated by the driving and processing circuit 27 intowireless transmission signals, and button-shaped batteries 29, 29 forsupplying power to the LED driving circuit.

An antenna 30 that is connected to the wireless communication circuit 28is located adjacent to the driving and processing circuit 27 and to thewireless communication circuit 28. Also, a non-contact-activated switch31 that can be activated in a non-contact manner and a permanent magnet32 for guiding the capsule endoscope 3 using magnetic power may beprovided, for example, adjacent to the batteries 29, 29 at the rear endof the capsule.

Two contact points with which the non-contact-activated switch 31 isturned on are positioned between one of the electrodes of the seriallyconnected batteries 29, 29 (for instance the positive electrode) and thecircuits to which electric power is supplied. Magnetic lines of forcehaving a specified direction may be applied from outside the capsule inorder to turn the two contact points to the ON state from the OFF state.When they are turned ON, an internal analogue switch is turned ON andremains in the ON state even when the applied magnetic lines of forceare removed. Therefore, the capsule endoscope 3 is able to maintain itsoperation state when the permanent magnet 32 is magnetized in order toguide the capsule endoscope 3.

The capsule endoscope 3 of this embodiment uses, as shown in FIG. 2(A),a semi-spherical transparent cover 17. The objective optical system 23is provided within the transparent cover 17 with its entrance pupil 34located at the center of curvature of the transparent cover 17. Morespecifically, the transparent cover 17 has inner and outer surfaceshaving the same center of curvature and with radii of curvature Ri andRo, for example, equal to 5 mm and 5.5 mm, respectively. Therefore, thethickness of the transparent cover 17 in this embodiment is uniform,making it easy to manufacture.

The objective optical system 23 is installed in the capsule so that itsentrance pupil 34 is centered about the same common point, and whiteLEDs 25 are positioned around the periphery of the objective opticalsystem 23.

The inner surface of the transparent cover 17 has an anti-reflectioncoating 35 applied thereto, such as transparent dielectric material.This efficiently reduces the amount of light from the illumination meansthat is undesirably reflected back toward the objective optical system,and thus improves the quality of the detected image data. In order toprevent undesired light from being reflected from the lens frame 22 (andother parts) and entering the objective optical system 23, the frontconical surface of the lens frame 22 and the front surface of thecircuit board 21 to which the white LEDs are affixed are provided with alight absorbing coating 36. Ideally the light absorbing coating is blackin color, but other known light absorbing means can be used, such asother dark-colored coatings, a matte or velvet surface, etc. In thisembodiment, the objective optical system 23 is capable of imaging withinthe visual field angle θ. The front surface of the lens frame has aconical cutout so that incident light within the visual field angle θcan enter the objective optical system 23.

With the above structure, when illumination light from the illuminationmeans is reflected on the inner surface of the transparent cover 17,very little undesired light that has been reflected from componentsother than the object of interest enters the objective optical system23.

FIG. 3 is an enlarged view of the objective optical system 23. Theobjective optical system 23 is formed of, in order from the object side,a first lens 37 that, for example, may be a plano-convex lens elementwith its planar surface on the object side, and a second lens 38 that,for example, may be a plano-convex lens with its convex surface on theobject side. A thin plate or black coating is placed on the frontsurface of the first lens 37 at the periphery of the entrance pupilposition 34 so as to form a brightness stop 39.

The image detecting means (i.e., CMOS image detecting element 24) ispositioned behind the second lens 38 with the center of its imagedetecting area aligned with the optical axis of the second lens 38 ofthe objective optical system 23. Light proceeding toward the entrancepupil position 34 is contracted by the brightness stop 39 and, as shownin FIG. 3, is imaged on the image plane of the CMOS image detectingelement 24.

The operation of this embodiment will now be described. By using apermanent magnet (not shown) which is brought near the rear portion ofthe capsule endoscope with the lines of force of the magnet having aspecified magnetizing direction, the non-contact-activated switch 31formed of a known, reed-type, switch is turned ON so as to place thecapsule endoscope in the operational state.

As will be described in detail, the capsule endoscope 3 then transmitsimage signals using the antenna 30. Antenna 12 (FIG. 1) receives theseimage signals and is connected to the external unit 5 which decodes theimage signals and displays them on a liquid crystal monitor 13. Afterconfirming that images captured by the capsule endoscope 3 are beingdisplayed on the liquid crystal monitor 13, a patient 2 is allowed toswallow the capsule endoscope 3.

Once swallowed, the capsule endoscope 3 begins its passage through thegastrointestinal tract. When the capsule endoscope 3 is in theoperational state, the control part of the driving and processingcircuit 27 sends control signals to the LED driving circuit that isformed on the circuit board 21. Then, the LED driving circuit directsthe white LEDs 25 to flash at a specific interval.

Light from the white LEDs 25 is transmitted through the transparentcover 17 so as to illuminate regions exterior to the capsule. Anilluminated object, such as the esophagus outside the transparent cover17, is imaged by the objective optical system 23 onto the CMOS imagedetecting element 24, which is positioned at the image plane of theobjective optical system 23. The CMOS image detecting element 24converts the image to image data in a known manner, depending on thetype of image detecting element that is used. Typically, a CMOS imagedetecting element 24 is used.

Synchronous with the flashing light (for instance, at the end of eachflash), the driving and processing circuit 27 sends control signals tothe CMOS image detecting element 24 so as to output photoelectricconverted signals. The driving and processing circuit 27 performs imageprocessing in which certain signal components are extracted and imagesignals are generated.

The generated image signals are transferred to the wirelesscommunication circuit 28 and used to modulate a high frequencyelectromagnetic wave so that the resultant wave can be transmitted viathe antenna 30. The electromagnetic wave is received via the antennaunit 4 that is provided outside the body of the patient 2 anddemodulated in the external unit 5 (in the reception part of thewireless communication circuit). It is then A/D converted, stored in ahard disk, and processed by the display circuit so as to display theimages captured by the CMOS image detecting element 24 on the liquidcrystal monitor 13.

When the capsule endoscope 3 approaches the main targeting part, forinstance—the small intestine (or when the time comes when the capsuleendoscope 3 is expected to approach an object of interest such as thesmall intestine), the control button 14 of the external unit 5 is usedto send a command signal from the external unit 5 to the capsuleendoscope 3 which causes the intervals between the flashing of theillumination means and the associated image detecting to shorten. Thus,the image data that is now captured at shorter intervals is temporarilystored on the hard disk of the external unit 5.

When the object is illuminated and imaged in the manner described above,the entrance pupil position 34 of the objective optical system 23 ispositioned with its center co-located with the center of the radii ofcurvature of the surfaces of the semi-spherical transparent cover 17.The white LEDs used as the illumination means are positioned at distantperipheral areas from the sphere center. Therefore, very littleillumination light from the illumination means enters the objectiveoptical system 23 even after a portion of this light is reflected fromthe inner surface of the transparent cover 17. This is illustrated withreference to FIGS. 4(A) and 4(B).

FIG. 4(A) is an illustration showing that light reflected by any pointP0 on the inner surface of the transparent cover 17 returns to thesphere center only when it is reflected by a surface having a normalthat passes through the point P0. Thus, if the light emitting areas ofthe white LEDs 25 were to overlap the sphere center, reflected lightwould return to the sphere center.

FIG. 4(B) is an illustration showing the case in which the sphere centerand the light emitting area of a light source do not overlap. In such acase, when light from the light source is reflected by any point P1 orP2 on the inner surface of the transparent cover 17, its angle ofreflection is equal to the angle of incidence, as shown (φ1 or φ2,respectively), and light is not returned to the sphere center.

As shown in FIGS. 4(A) and 4(B), the white LEDs 25 used as theillumination means are located somewhere other than the sphere center ofthe transparent cover 17. This prevents light reflected by thetransparent cover 17 from passing through the sphere center position ofthe transparent cover 17 or from entering the entrance pupil position 34of the objective optical system 23. Therefore, flare and ghosting thatresults from light being reflected on the inner surface of thetransparent cover 17 and entering the objective optical system 23 can beeffectively prevented.

Further, observations can be performed by overlapping an area within theimage plane 100 of a CMOS image detecting element 24, that is not usedfor image detection, with an area that is symmetrically opposed, aboutthe optical axis of the objective optical system, to a light emittingarea of a white LED 25. This embodiment uses a CMOS image detectingelement as the solid-state image detecting element (image sensor).However, the type of solid-state image detecting element is notrestricted to a CMOS image sensor, and it is apparent that other imagesensors, such as CCDs and the following three, more recently developedbut known, image sensors can be used. Each has advantages, as describedbelow.

The first image sensor is a next generation image sensor termed a“threshold modulated image sensor (VMIS)” that has the advantages ofboth CCD and CMOS image detecting elements. Unlike prior art CMOS imagedetecting elements in which the light receiving part for each pixelconsists of three to five transistors and photodiodes, electric chargethat is generated by received light modulates the threshold of the MOStransistor. Modulation in the threshold is output as image signals. Thistype of image sensor is characterized by a combination of high imagequality as provided by a CCD image sensor with the higher degree ofintegration, lower driving voltage, and lower power consumption of aCMOS image sensor. Therefore, a VMIS-type image sensor is particularlywell-suited for use in a disposable capsule endoscope. Other beneficialcharacteristics of a VMIS-type image sensor are: a simple structure thatuses only one transistor per image sensor pixel, excellent photoelectricproperties such as a high sensitivity and a high dynamic range, and ahigh density and low price due to the manufacturing techniques being thesame as in making a CMOS transistor. Exemplary sensor types include QCIF(QSIF) size, CIF(SIF) size, VGA type, SVGA type, XGA type. Smaller sizesensors, such as the QCIF (QSIF) the CIF(SIF) size sensors areespecially suitable for the capsule endoscope of the present invention,in terms of the wireless transmission rate, low power consumption, andsmall size, making the capsule easier to swallow.

The second type of image sensor is termed an ‘artificial retina LSI’ andis basically a CMOS image sensor that is integrated with an imageprocessing circuit into a chip. This chip simultaneously detects imagesand performs some image processing, as apparently is similar to thefunctions performed by the human eye. Conventional CCD and CMOS imagesensors only detect images. External image processors are then used toperform characterization and verification processes. The artificialretina chip itself performs these processes. Therefore, the circuit canbe simplified and downsized. Further advantages include ahigh-throughput process, a single power source, and low powerconsumption. Therefore the ‘artificial retina LSI’ is suitable for usein disposable capsule endoscopes. Other beneficial characteristics ofthis type of image sensor include: the ability to conduct image contourextraction, white balance, edge enhancement, brightness adjustment,built-in gamma correction function, and built-in A/D conversionfunction; high sensitivity and high image quality; a small-sizedpackage; and a built-in noise reduction circuit is available. Exemplarysensor types include QCIF (QSIF) size, 160×144 size, CIF(SIF) size, VGAtype, SVGA type, XGA type. Smaller ones such as QCIF (QSIF) size,160×144 size, and CIF(SIF) size are especially suitable for use in thecapsule endoscope of the present invention in terms of wirelesstransmission rate, low power consumption, and small-size, making thecapsule easy to swallow.

The third type of image sensor is a color image sensor having threephoto detectors (light receiving layers) arranged in the depth(lengthwise) for each pixel so as to obtain respective RGB colorsignals, wherein different layers absorb light having differentwavelengths. This allows the resolution to be doubled compared toconventional image sensors that use the same number of pixels. This typeof image sensor has advantages similar to that of CCDs. The sametechnology can also be applied to a CMOS image sensor, and the price ofsuch units should become competitive to that of conventional imagesensors. The color image sensor uses a VPS (Variable Pixel Size) systemthat reads several pixels collectively to read respective color signals.This advantageously allows the pixel size to change. This also providesadvantages such as high sensitivity for still images and high readingrates required for video images (motion images).

With this type of color image sensor, no false colors are produced.Therefore, it can be used without a low pass filter. This type of colorimage sensor is suitable for capsule medical devices that require asmall size and a low power consumption. It is also suitable forconventional video endoscopes.

The present invention uses wireless transmissions that are conductedaccording to the BLUETOOTH standard. However, the invention is notrestricted to using the BLUETOOTH standard, and a broad band, wirelesspulse technique that is currently under development will obviously beapplicable to the invention. Broadband has the following advantages: thesignal is diffused using a broad band, wireless communication with thesignal approaching that of the noise level; therefore, broadbandcommunication can be used in conjunction with a conventional narrow-bandcommunications, and unlike narrow-band communication, carrierfrequencies are not used. Therefore, signals can be directly analyzed.For instance, precise distance information is easily retrieved bymeasuring arrival times. Precise distance information gives one preciselocation information.

Recently, a pulse wireless communication technology called UWB (UltraWide Band) was released and is being commercialized. If incorporated inthe wireless communication device of a capsule medical system, the UWBtechnology allows the use of long wavelengths which are more easilytransmitted through the human body. Better transmittance through thehuman body means that much less power supply is required and, thus,power consumption of the wireless communication device can be reduced.Also with using such a wireless technology, precise position informationis also obtained.

Embodiment 2

Embodiment 2 of the present invention will now be described withreference to FIG. 5. FIG. 5 is a schematic view showing the structure ofthe capsule endoscope 3B of Embodiment 2. The thickness of thetransparent cover 17B in this embodiment is no longer uniform. Instead,the transparent cover 17B is thicker on axis and tapers so as becomethinner toward the peripheral regions of the field of view. Thetransparent cover 17B is provided with an inner surface having a radiusof curvature Ri, for example, equal to 5.5 mm within the visual fieldangle θ, with the center of curvature coinciding with the center of theentrance pupil 34 of the objective optical system 23.

On the other hand, the outer surface of the transparent cover 17B has aradius of curvature Ro, for example, equal to 5.5 mm within the visualfield angle θ. The center of curvature of the outer surface is locatedon the optical axis but is positioned on the object side of the entrancepupil position 34 of the objective optical system 23. In this case, thedistance between the center of curvature of the outer surface and theon-axis position of the entrance pupil is 0.5 mm.

The inner surface of the transparent cover 17B is composed of twodifferent curved surfaces. One is a spherical surface having a radius ofcurvature Ri. The other is a doughnut-like surface, with the radius ofthe doughnut ring being Rs, with Rs<Ri. The centers of these radii arepositioned, in cross-section, as illustrated in FIG. 6. Thus, thethickness of the transparent cover reduces from a maximum at the centerof the visual field to a minimum at the periphery of the visual field,namely, the contact position of the two different curved surfaces. Dueto the small value of Rs (i.e., 3 mm) reduction of the thickness of thecover ceases slightly outside the visual field. Then the cover isconnected to the cylindrical portion 17C. When the portion in which theouter radius is Ro and the inner radius is Rs is wide, the thicknessreduction of the cover first ceases and then begins to graduallyincrease. But actually the portion is narrow. Therefore, at a positionwhere the reduction of the thickness almost ceases—this is the portionwhere the thickness becomes nearly uniform—the cover 17B is connected tothe cover 17C. One advantage of using a transparent cover 17B that isthicker in the center, is that the cover is made stronger and is lesslikely to break, should the capsule be subjected to a mechanical shock.However, there is a second advantage of the transparent cover 17B havinga thickness within the visual field angle θ that gradually decreasestoward the periphery, in that light reflected by the outside surface ofthe cover will tend to be guided by being reflected by the inner andouter surfaces until being released at the periphery of the visualfield. Thus, undesired light is further prevented from entering theimage detecting means, providing excellent observed images. Thisphenomenon will be explained in greater detail with reference to FIG. 6.

As shown in FIG. 6, a portion of the illumination light from a lightsource that is transmitted through the inner surface will be reflectedby the outer surface of the transparent cover 17B. Part of this lightwill pass through the inner surface and contribute to stray light thatis detected by the image detecting element. Some of the illuminationlight that is reflected by the outer surface will be totally internallyreflected at the inner surface of the transparent cover and will againreach the outer surface of the transparent cover 17B. Moreover, when thetransparent cover 17B has a coating such as an anti-reflection coating,the refractive index of the coating should be taken into account. Thiswill not be further discussed, other than to state that a portion of thereflected light from the outer surface of the transparent cover 17B willbe repeatedly totally internally reflected between the inner and outersurfaces of the transparent cover. As shown in FIG. 6, the angle ofincidence onto the-surfaces decreases with each reflection until suchtime that the light is no longer totally internally reflected and isreleased into the air at peripheral areas of the transparent cover 17B.Thus, tapering the thickness of the transparent cover so that it becomesthinner toward the periphery of the visual field angle θ is helpful inreducing stray light that otherwise degrades the images detected by theimage detecting means. The radii of curvature of the inner and outersurface within the visual field angle θ can be determined according tothe refractive index of the transparent cover 17B so that light thatinternally reflects within the transparent cover escapes from thetransparent cover 17B into the air layer outside the visual field angleθ of the objective optical system 23. This can prevent the adverseeffect of flare in the visual field caused by the reflected light fromthe outer surface of the transparent cover 17B. As described previously,near the periphery of the transparent cover, the curvature of thetransparent cover can be increased in a doughnut-shaped region so as tohave an apparent radius of curvature, in cross-section, of Rs, where Rsis less than Ro. This enables the length of the transparent cover, andthus of the capsule endoscope itself, to be decreased for a givencylinder diameter of the capsule body.

The objective optical system can serve to correct optical aberrations atthe image plane that are caused by the above-discussed tapering inthickness of the transparent cover within the visual field angle θ.Also, in this embodiment, the CMOS image detecting element 24 is coveredon its front side by a cover glass 41.

FIG. 7 is an illustration showing the structure of a Modification 1 thatcan be made to Embodiment 2. The transparent cover in this modificationhas an outer surface with a radius of curvature Ro equal to, forexample, 5.5 mm. This curvature continues nearly to the periphery of thevisual field. As before, the center of curvature of the outer surface islocated on axis on the object side of the entrance pupil position 34, asillustrated, but in this instance the distance is greater so thetransparent cover is thicker on axis. As before, the transparent coverhas an inner surface that is a combination of a spherical surface and adoughnut-shaped surface. The spherical portion of the inner surfacecovers the central region of the visual field and extends almost to theperiphery of the visual field. It has a radius of curvature Ri of, forexample, 6 mm, and the center of curvature of the spherical region ofthe inner surface is on-axis at the entrance pupil position of theobjective optical system. The doughnut-shaped portion of the innersurface begins near the periphery of the visual field. As before, thecenter of the doughnut is on axis and is positioned on the object sideof the entrance pupil position 34, with the radius of curvature of thering of the doughnut being Rs, as illustrated in cross-section in FIG.7. As before, Rs<Ri, and the thickness of the transparent coverdecreases from a maximum at the center of the visual field toward theperiphery. Due to the small value of Rs (i.e., 3 mm) reduction of thethickness of the cover ceases slightly outside the visual field. Thetransparent cover portion 17C is then engaged with the leading edge ofthe outer cover 16 and sealed in a watertight manner.

Modification 1 effectively prevents the illumination light from thewhite LEDs 25 from entering the objective optical system 23 even if itis reflected by the inner surface of the transparent cover 17C. Inaddition, by having the thicker center part, the transparent cover 17Cis made more sturdy and is better able to withstand mechanical shocks.

FIGS. 8 and 9 show the structures of the capsule endoscopes 3D and 3E ofModifications 2 and 3, respectively, to this embodiment. In the capsuleendoscopes 3D and 3E, the transparent covers 17D and 17E, respectively,have an outer surface with a radius of curvature Ro (for example, Ro=5.5mm) and the center of curvature of the outer surface coincides with theaxial position of the entrance pupil position 34. The centers ofcurvature of the inner surfaces of the transparent covers 17D and 17Elie to the image-side of the axial positions of the entrance pupilpositions 34, 34. For example, the transparent cover 17D has an innersurface radius of curvature Ri of 5.5 mm and the transparent cover 17Ehas an inner surface radius of curvature Ri of 6 mm. Modifications 2 and3 use an anti-reflection coating 35 to effectively prevent theillumination light from the white LEDs 25 from being reflected by theinner surface of the transparent cover 17D or 17E.

Embodiment 3

FIG. 10(A) is a cross-sectional view of an capsule endoscope 51 ofEmbodiment 3 of the present invention. FIG. 10(B) is an illustrationshowing the positional relationship between the illumination means andthe image detecting element when viewing the capsule endoscope axiallyfrom the object side. Referring to FIG. 10(A), the capsule endoscope 51includes a transparent front cover 52 that has a cylinder form with asemi-spherical front end and a rear cover 53 which also is shaped as acylinder that has a semi-spherical rear end. The rear end of thetransparent front cover 52 and the front end of the rear cover arefitted to each other and sealed so as to create a watertight capsulecontainer in which an objective optical system 54 and other elements arehoused.

The objective optical system 54 is formed of a first lens supported by afirst lens frame 55 and a second lens supported by a second lens frame56, and is positioned along the axis of symmetry of the capsule with itsentrance pupil 75 facing the front cover 52. A CMOS image detectingelement 58 is affixed onto the front surface of a circuit board 57 andis positioned at the image surface formed by the objective opticalsystem 54. White LEDs 60 are provided on a circuit board 59 which isengaged with, and fixed to, the second lens frame 56. As shown in FIG.10(B), a white LED 60 that is ring-shaped is centered about the opticalaxis 101 of an objective optical system. A portion of the ring-shaped,white LED 60 overlaps an area (shown with cross-hatching in FIG. 10(B))of the image plane 100 of a CMOS image detecting element 58 that is notused for image detection. The circuit board 57, on which the CMOS imagedetecting element 58 is mounted, is electrically connected via aconnector 61 to a circuit board onto which other electronic elements aremounted so as to form a driving and processing circuit 62. A circuitboard that includes a memory circuit 63 and other electronic componentsis positioned behind and connected, via a connector 64 to the circuitboard on which the driving and processing circuit 62 is mounted. Acircuit board that supports a wireless communication circuit 65 ispositioned behind and connected via a connector 66 to the circuit boardthat Supports the memory circuit 63. Two button-shaped batteries 67 arepositioned behind the circuit board that supports the wirelesscommunication circuit 65.

An antenna 68 is positioned adjacent to the circuit board that supportsthe driving and processing circuit 62. For instance, a negativeelectrode of the serially connected batteries 67, 67 is connected to theground of the wireless communication circuit 65 and to the ground of theother circuits via a lead (not labeled). The positive terminal of thewireless communication circuit 65 and the positive terminals of theother circuits are connected to one end of a spring contact member 71.The spring contact member 71 includes a contact part 71a positionedbehind the serially connected batteries 67, 67. An insulating plate 73is detachably positioned between the contact part 71a of the springcontact member 71 and the contact part 71b that contacts the positiveelectrode of the batteries. Thus, because the insulating plate 73prevents electrical contact between the contact part 71a and the contactpart 71b, the OFF state of the capsule endoscope is established.

Part of the insulating plate 73 extends through the capsule endoscopewall via a small cut-out part which has a rubber valve part 74. Bypulling out the insulating plate 73, the spring-biased contact part 71ais allowed to contact the contact part 71b so as to establish the ONstate. The rubber valve part 74 automatically seals closed so as tomaintain a watertight condition once the insulating plate 73 is pulledout from the capsule endoscope. The transparent dome part of the frontcover 52 has inner and outer surfaces with constant radii of curvatureRi and Ro, respectively, that extend nearly to the periphery of thevisual field θ. In this embodiment, Ri is 6.0 mm and Ro is 6.5 mm. Thecenters of curvature of both the inner and outer surfaces of the domecoincide with the axial position of the entrance pupil 75 of theobjective optical system 54. Thus, this embodiment uses a transparentdome having a uniform thickness within the central part of the visualfield θ. Near the periphery of the visual field θ, the outer surface ofthe transparent dome has a radius of curvature Rp that is smaller thaneither of the radii of curvature Ri and Ro (for instance Rp=4.0 mm) sothat the outer surface continues until it meets the cylindrical body ofthe capsule. The capsule endoscope 51 of this embodiment has an outerbody diameter D of 11 mm. The first lens frame 55 has a conical frontsurface 76 that is roughened so as to diffuse light that is incidentthereon. Due to the arrangement of the components and the design of thetransparent cover, this embodiment, also effectively prevents a portionof the illumination light that is reflected from the inner and outersurfaces of the front cover 52 from entering the objective opticalsystem 54. In other words, it effectively prevents undesired light fromentering the objective optical system 54, thereby achieving excellentquality images.

Embodiment 4

FIG. 11(A) shows, in cross-section, the structure of the capsuleendoscope 81 of Embodiment 4 of the present invention. FIG. 11(B) showsthe ON state of the capsule endoscope of this embodiment. FIG. 11(C)shows the positional relationship between the illumination means and theimage detecting element when viewing the capsule endoscope axially fromthe object side, and FIG. 11(D) shows a possible modification to thepositional relationship shown in FIG. 11(C).

The capsule endoscope 81 of this embodiment includes a cylindrical outercover 82 having a closed, rounded rear end and a front end with which anearly semi-spherical transparent cover 83 is engaged and sealed tocreate a watertight structure in which an objective optical system 84and other elements are housed. The objective optical system 84 is formedof, in order from the object side, a first lens that is supported by afirst lens frame 85 and a second lens that is supported by a second lensframe 86. A CCD 88, that is positioned within a recess provided on thefront surface of a circuit board 87, is positioned with its detectingsurface at the image plane of the objective optical system 84. WhiteLEDs 91 are attached to a circuit board 90 that is fixed to the barrelof the second lens frame 86 which engages with the first lens frame 85.

As shown in FIG. 11(C), the white LED 91 is arranged so that, as viewedfrom the front of the capsule, the area on the image detecting surfacethat is symmetrically opposed about the optical axis 101 to the whiteLED 91 is not used for image detection. However, this area may be anactive area of the CCD that is used for detecting ‘optical black’. Theoptical black portion is an area where the picture elements are shieldedby masking (physically or electrically) the image detecting surface 100and thus is an area not used for image detection. In addition, as shownin FIG. 11(D), two white LEDs 91 may be used with an image detectingelement. In this instance a different type CCD 88′ is used. The CCD 88′comprises an optical black component (that portion of CCD 88′ which isshown with diagonal lines and is not used for image detection) and asignal reading component. Accordingly, the white LEDs 91 are arranged sothat areas (namely, the areas shown by the diagonal lines in FIG. 11(D)that are symmetrically opposed about the optical axis 101 of theobjective optical system to the LEDs 91 overlap with an area of theimage detecting element that is not used for imaging. FIGS. 11(C) and11(D) have been simplified for purposes of explanation by showing fewerLED's 91 than may actually exist.

Behind the circuit board 87 on which the CCD 88 is mounted, a circuitboard 92 is positioned on which electronic components are mounted thatform a driving, processing and memory circuit. Behind the circuit board92 there is a circuit board which Supports a wireless communicationcircuit 93. Electronic chip elements 94, 94 and components of thewireless communications circuit 93 are mounted on both sides of thecircuit board. Button-shaped batteries 67 are provided behind thecircuit board that supports the wireless communications circuit 93. Anantenna 95 is positioned adjacent to the circuit boards 87 and 92.

As shown in FIGS. 11(A) and 11(B), the serially connected batteries67,67 have their positive electrode in electrical contact with a contactpart 71b. As previously described with regard to FIG. 10(A), springcontact member 71a, is prevented from contacting contact part 71b by aninsulating plate 73 that is positioned between these members, so thatthe OFF state is established. By pulling out the insulating plate 73,the contact parts 71a and 71b are allowed to contact each other so as toestablish the ON state.

This embodiment uses a transparent cover 83 having, within the visualfield θ, inner and outer surfaces with radii of curvature Ri and Roequal to 4.5 mm and 5.0 mm, respectively. Both the inner and outersurfaces of the transparent cover 83 have a common center of curvaturethat is positioned at the axial position of the entrance pupil 96 of theobjective optical system 84. Thus, within the visual field θ in thisembodiment, the transparent cover 83 has a uniform thickness of 0.5 mm.Outside the visual field θ the curvature of the transparent cover outerand inner surfaces is different (with the outer surface having anapparent radius of curvature, as seen in cross-section, of Rp) so thatthe transparent cover fits smoothly to a capsule endoscope body havingan outer diameter of 11 mm. Such a design enables the overall capsulelength to be shortened. Furthermore as noted above, the front end of thetransparent cover has a smaller radius of curvature than one-half thevalue of the outer diameter of the capsule endoscope 81. Thiscontributes to a reduced overall length of the capsule endoscope 81.Also, this embodiment uses a cylindrical first lens frame 85. The firstlens, fixed within the first lens frame 85, has a front surface that isprovided with a thin plate or a coating for shielding light around theentrance pupil position 96 so as to form a brightness stop 97.

One feature of this embodiment is that the position of engagement of thetransparent cover to the capsule can be adjusted lengthwise beforesealing so that the entrance pupil position 96 of the objective opticalsystem 84 coincides with the center position of the radii of curvatureRi and Ro of the transparent cover 83. In other words, the portion ofthe transparent cover 83 that engages with the cylindrical outer cover82 can be used as a positioning means to locate the entrance pupilposition 96 of the objective optical system 84 at the center ofcurvature, within the visual field θ. Providing a positioning meansensures precise positioning of the entrance pupil position 96 of theobjective optical system 84 at the center position of the radii ofcurvature Ri and Ro of the transparent cover 83. The positioningadjustment can be conducted using an optical adjusting apparatus (notillustrated). Also, the positioning can be conducted by operating thecapsule endoscope and positioning the transparent cover to a positionwhere flare light is minimized. The structure for positioning that isdisclosed in other embodiments is also applicable to this embodiment.

Embodiment 5

FIG. 12(A) is a cross-sectional view of the tip portion of the capsuleendoscope according to Embodiment 5 of the present invention. FIG. 12(B)illustrates the positional relationship between the image detectingmeans and the illumination means when viewing the capsule endoscopeaxially from the object side. FIG. 12(C) is an illustration showing thepositional relationship between the image detecting means and theillumination means when viewing the capsule endoscope axially from theobject side in a modified example of Embodiment 5.

In a capsule endoscope according to the present embodiment, thetransparent cover 110 has its outer and inner surfaces semi-spherical inshape with a common center of curvature, and the objective opticalsystem 112 is arranged inside the capsule so that the center of itsentrance pupil coincides with the common center of curvature of thetransparent cover 110, as shown in FIG. 12(A). The image detectingsurface 100 (FIG. 12(B)) of a CCD 113 is arranged at the image plane ofthe objective optical system 112. Four white LEDs 111 are attached atthe periphery of the objective optical system 112. Further, as shown inFIG. 12(B), miniaturization of the capsule endoscope is achieved bydetermining the positional relationship between the white LEDs and theCCD 113 so that a peripheral area 114 (shown by cross-hatching in FIG.12(B)) of the CCD that is electrically masked so as to not provide imagesignals from these areas is symmetrically opposed to the white LEDs 111about the optical axis 101. This electrical masking is illustrated as ifan actual physical mask were placed on the image plane 100, but, infact, it is implemented by ignoring, for image-formation purposes, imagepixel data in the areas indicated.

The electrically-implemented mask 114 in this embodiment has the effectof there being a round shape that is projected onto the image plane 100,since distortion aberration of the objective optical system 112 iscorrected. An area inside the electrically-implemented mask 114 is thearea used for imaging.

A first modified example of Embodiment 5 is shown in FIG. 12(C). In FIG.12(C), the electrically-implemented mask 114 is a more complex shape, inorder to account for the objective optical system 112 generatingnegative distortion. In this modified example, four white LEDs 111,which form the illumination means for this embodiment, are arranged withtheir centers near the four corners of the CCD 113. The four white LEDs111 are positioned relative to the CCD 113, as viewed axially from thefront of the capsule endoscope, so that an area that is symmetricallypositioned about the optical axis of the objective optical system from alight emitting area of the illumination means overlaps an area of theCCD 113 but does not overlap any area of the CCD 113 that is used forpicture imaging. By arranging the LEDs as above and electrically maskingthe area as indicated to account for negative distortion created by theobjective optical system 112, a small-scale capsule endoscope can beprovided that has the ability to observe images while avoidingover-exposure. This is accomplished by masking (electrically orotherwise) those pixel elements which otherwise would be over-exposed bythe detected light containing a high proportion of specularly reflectedlight. This specularly reflected light arises both from light that isreflected at the transparent cover inner and outer surfaces, and fromlight that is reflected from lumen wall surfaces, especially lumen wallsurfaces that contact the peripheral portions of the transparent cover.

A second modified example of Embodiment 5 is shown in FIGS. 13(A) and13(B). As shown in FIG. 13(A), a capsule endoscope having left and rightobjective optical systems for capturing images having parallax isprovided, so that images for 3-D displays can be captured by the capsuleendoscope. In this modified example of Embodiment 5, the exit pupil ofan illumination means is placed at the center of curvature of thetransparent cover, and left and right objective optical systems are usedon either side of the illumination means.

The capsule endoscope according to this modification to Embodiment 5employs a transparent cover 120 having a front portion that issemi-spherical in shape, as shown in FIG. 13(A). An output pupil of alight diffusion means 123 is arranged in front of a white LED 122 whichis placed along the central axis of the cylindrical-shaped centerportion of the capsule body. The center of the output pupil of the lightdiffusion means 123 is preferably placed so as to coincide with thecenter of curvature of the inner and outer surfaces of the transparentcover 120. The objective optical systems 125 and 126 are arranged onopposite sides of the white LED 122, and the image detecting surfaces(FIG. 13(B)) of CCDs 127 and 128 are arranged at the image planes 100and 100′ of respective objective optical systems 125 and 126. Inaddition, white LEDs 129a and 129b (not illustrated in FIG. 13(A)) maybe positioned as indicated in FIG. 13(B), where a line segmentconnecting the centers of the LEDs 129a and 129b intersect, a linesegment connecting the centers of the image detecting elements 118 and119, and the central axis 117 of the diffusion means intersect at acommon point.

Further, as shown in FIG. 13(B), peripheral areas outside the dottedlines labeled 130 and 130′ that include portions of regions of 131a,131a′, 131b, 131b′ that are symmetrically positioned about the opticalaxis of each objective optical system from light emitting areas ofillumination means (namely, the non-centered LEDs 129a and 129b), aswell as regions which take into account the negative distortion of theobjective optical systems 125 and 126, are electrically masked so thatthey do not contribute to the image detected by the image detectingelements 127 and 128.

By electrically masking selected areas of the image detecting elements127 and 128 in this manner, even in a capsule endoscope having aplurality of image detecting elements and a plurality of illuminationmeans, it is possible to obtain properly exposed images containingparallax of a viewed object by, in effect, ignoring those pixel areas ofthe image detecting elements of the image sensors that will beover-exposed as a result of either the transparent cover or an object ofinterest specularly reflecting a proportion of the illumination lightinto the image sensor via the objective optical systems.

FIGS. 14(A) and 14(B) relate to a third possible modification toEmbodiment 5, with FIG. 14(A) being a cross-sectional view of theconstruction of the main components of the tip portion of a capsuleendoscope comprising a plurality of objective optical systems, and withFIG. 14(B) showing the positional relationship between the illuminationmeans and the imaging means when viewing the capsule endoscope axiallyfrom the object side. Once again, an output pupil of a light diffusionmeans 143 is arranged in front of a white LED 142 which is placed alongthe central axis 140 of the cylindrical-shaped center portion of thecapsule endoscope body. The center of the output pupil of the lightdiffusion means 143 is preferably placed so as to coincide with thecenter of curvature of the inner and outer surfaces of the transparentcover 141. The objective optical systems 144 and 145 are arranged onopposite sides of the white LED 142, and the image plane of a shared CCD146 is positioned to be co-planar with the image planes of the objectiveoptical systems 144 and 145. In addition, white LEDs 149a and 149b (notillustrated in FIG. 14(A) but shown in FIG. 14(B)) may be positioned asindicated (i.e., symmetrically about the LED 142, as viewed from thefront of the capsule).

Further, as shown in FIG. 14(B), peripheral areas outside the dottedlines labeled 150 and 150′ that include portions of regions 151a, 151a′,151b, 151b′ that are symmetrically positioned about the optical axis ofeach objective optical system from light emitting areas of illuminationmeans (namely, the non-centered LEDs 149a and 149b), as well as regionswhich take into account the negative distortion of the objective opticalsystems 144 and 145, are electrically masked so that they do notcontribute to the images detected by the shared image detecting element146.

By electrically masking selected areas of the image detecting element146 in this manner, even in a capsule endoscope having a plurality ofillumination means, it is possible to obtain properly exposed imagescontaining parallax of a viewed object by, in effect, ignoring thosepixel areas of the image detecting element that will be over-exposed asa result of light being specularly reflected by the transparent coversurfaces or a lumen wall that is in contact at a peripheral region ofthe transparent cover into the image detecting element via the objectiveoptical systems.

In all of the embodiments, the anti-reflection coating on the innersurface of tile transparent cover is advantageous in reducing undesiredlight that would otherwise indirectly enter the objective optical systemvia the inner surface of the transparent cover from outside the visualfield, as well as in reducing undesired light that enters the visualfield directly. In addition, a water repellant coating on the outersurface of the transparent cover prevents contaminants from adhering tothe transparent cover, thereby obstructing observations.

Of course, it is essential that the transparent cover and the capsuleendoscope body are made of materials that are not harmful to humans.Further, it is important that all of the components of the capsuleendoscope do not harm the environment when disposed of in a low costmanner. In this way, a capsule endoscope that is disposable after eachuse may be provided at a reasonably low cost.

The invention being thus described, it will be obvious that the same maybe varied in many ways. For example, combinations of the featuresdescribed in the preferred embodiments may be selectively used. Rather,the scope of the invention shall be defined as set forth in thefollowing claims and their legal equivalents. All such modifications aswould be obvious to one skilled in the art are intended to be includedwithin the scope of the following claims.

1. A capsule endoscope, comprising: illumination means that includes alight emitting element for illuminating an object; imaging means forimaging the object; and a transparent cover having a center ofcurvature, said transparent cover covering the illumination means andthe imaging means; wherein the imaging means includes an objectiveoptical system and an image detecting element; an entrance pupilposition of the objective optical system is arranged so that its centeris located substantially at the center of curvature of the transparentcover; and the illumination means is positioned relative to the imagedetecting element, when viewing the capsule endoscope from the objectside, so that an area that is symmetrically positioned about the opticalaxis of the objective optical system from a light emitting area of theillumination means overlaps an area of the image detecting element butdoes not overlap any area of the image detecting element that is usedfor picture image detection.
 2. The capsule endoscope according to claim1, wherein an area of the image detecting element that is not used forpicture imaging and which is symmetrically positioned, when viewing thecapsule endoscope from the object side, about the optical axis of theobjective optical system from a light emitting area of the illuminationmeans is a mask area that is treated electrically at the time of thepicture image processing.
 3. The capsule endoscope according to claim 1,wherein the transparent cover has an inner surface and an outer surface,the center of curvature of the inner surface being located substantiallyat the entrance pupil position; and the transparent cover has athickness that, from a maximum opposite the entrance pupil, decreasestoward the periphery of the transparent cover.
 4. A capsule endoscope,comprising: illumination means that includes a light emitting elementfor illuminating an object; imaging means that includes an objectiveoptical system for imaging the object; and a transparent cover having acenter of curvature, said transparent cover covering the illuminationmeans and the imaging means; wherein the illumination means includes anillumination diverging means having an exit pupil, and a light emittingelement, and the center of the exit pupil of the illumination divergingmeans is arranged to substantially coincide with the center of curvatureof the transparent cover.
 5. The capsule endoscope according to claim 4,wherein the imaging means comprises a plurality of lens elements thatconstitute the objective optical system, and an image detecting element.6. A capsule endoscope, comprising: illumination means for illuminatingan object; imaging means for imaging the object; and a transparent coverhaving a center of curvature, said transparent cover covering theillumination means and the imaging means; wherein the imaging meansincludes a plurality of objective optical systems and an image detectingelement; the illumination means include illumination diverging meanshaving exit pupils and light emitting elements; one exit pupil of theillumination diverging means is arranged so as to substantially coincidewith the center of curvature of the transparent cover, and the remainingexit pupils of the illumination diverging means are positioned relativeto the image detecting element, when viewing the capsule endoscope fromthe object side, so that areas that are symmetrically positioned aboutthe optical axes of the objective optical systems from the exit pupilsof the remaining illumination diverging means overlap areas of the imagedetecting element but do not overlap any area of the image detectingelement that is used for picture image detection.
 7. The capsuleendoscope according to claim 6, wherein an area of the image detectingelement that is not used for picture imaging and which is symmetricallypositioned, when viewing the capsule endoscope from the object side,about the optical axes of the objective optical system from a lightemitting area of the illumination means is a mask area that iselectrically masked at the time of the picture image processing.
 8. Acapsule endoscope, comprising: illumination means for illuminating anobject; imaging means for imaging the object; and a transparent coverhaving a center of curvature, said transparent cover covering theillumination means and the imaging means; wherein the imaging meansincludes a plurality of objective optical systems and a plurality ofimage detecting elements; the illumination means include illuminationdiverging means having exit pupils, and light emitting elements; theexit pupil of one illumination diverging means is arranged tosubstantially coincide with the center of curvature of the transparentcover, and the exit pupils of the remaining illumination diverging meansare positioned relative to the image detecting elements, when viewingthe capsule endoscope from the object side, so that areas that aresymmetrically positioned about the optical axes of the objective opticalsystems from the exit pupils of the remaining illumination divergingmeans overlap areas of the image detecting elements but do not overlapany area of the image detecting elements that is used for picture imagedetection.
 9. A capsule endoscope, comprising: illumination means thatincludes a light emitting element for illuminating an object; imagingmeans for imaging the object; and a transparent cover which covers theillumination means and the imaging means; wherein the imaging meansincludes an objective optical system and an image detecting element, theillumination means is positioned relative to the image detectingelement, when viewing the capsule endoscope from the object side, sothat an area that is symmetrically positioned about the optical axis ofthe objective optical system from a light emitting area of theillumination means overlaps an area of the image detecting element butdoes not overlap any area of the image detecting element that is usedfor picture image detection.
 10. The capsule endoscope according toclaim 9, wherein an area of the image detecting element that is not usedfor picture imaging and which is symmetrically positioned, when viewingthe capsule endoscope from the object side, about an optical axis of theobjective optical system from a light emitting area of the illuminationmeans is a mask area that is electrically masked at the time of thepicture image processing.
 11. The capsule endoscope according to claim9, wherein: the objective optical system has an entrance pupil; thetransparent cover has an outer surface, the center of curvature of theouter surface being located substantially at the entrance pupilposition; and the transparent cover has a thickness that, from a maximumopposite the entrance pupil, decreases toward the periphery of thetransparent cover.
 12. A capsule endoscope, comprising: illuminationmeans that includes a light emitting element for illuminating an object;imaging means for imaging the object; and a transparent cover having acenter of curvature, said transparent cover covering the illuminationmeans and the imaging means; wherein the imaging means includes anobjective optical system and an image detecting element; an entrancepupil position of the objective optical system is arranged so that itscenter is located substantially at the center of curvature of thetransparent cover; and the illumination means is positioned off of thecenter of curvature, whereby light from the illumination means which isinternally reflected by the transparent cover does not pass through thecenter of curvature and does not enter the entrance pupil position ofthe objective optical system.
 13. The capsule endoscope according toclaim 12, wherein the illumination means includes a plurality of lightemitting elements which are arranged around the center of curvature,near the periphery of the transparent cover.
 14. The capsule endoscopeaccording to claim 12, wherein the transparent cover has asemi-spherical shape with a uniform thickness.
 15. The capsule endoscopeaccording to claim 14, wherein the entrance pupil position is arrangedso that it is located substantially at the center of curvature, within aspecified visual field, of both an inner surface and an outer surface ofthe transparent cover.
 16. The capsule endoscope according to claim 12,wherein the transparent cover has a semi-spherical shape.
 17. Thecapsule endoscope according to claim 16, wherein the thickness of thetransparent cover is thicker on the optical axis of the objectiveoptical system and tapers so as to become thinner toward the peripheralregions of the field of view.
 18. The capsule endoscope according toclaim 12, wherein the illumination means comprises an even number ofLEDs arranged around the periphery of the objective optical system. 19.A capsule endoscope, comprising: illumination means that includes alight emitting element for illuminating an object; imaging means forimaging the object; and a transparent cover having a center ofcurvature, said transparent cover covering the illumination means andthe imaging means; wherein the imaging means includes an objectiveoptical system and an image detecting element; an entrance pupilposition of the objective optical system is arranged so that its centeris located substantially at the center of curvature of the transparentcover; and the illumination means is positioned somewhere else than thecenter of curvature, whereby light from the illumination means that isreflected by the inner surface of the transparent cover is not returnedto the center of curvature and does not enter the entrance pupilposition of the objective optical system.
 20. The capsule endoscopeaccording to claim 19, wherein the illumination means includes aplurality of light emitting elements which are arranged around thecenter of curvature, near the periphery of the transparent cover. 21.The capsule endoscope according to claim 19, wherein the transparentcover has a semi-spherical shape with a uniform thickness.
 22. Thecapsule endoscope according to claim 19, wherein the entrance pupilposition is arranged so that its center is located, within a specifiedvisual field, substantially at the center of curvature of the innersurface of the transparent cover.
 23. The capsule endoscope according toclaim 22, wherein the transparent cover has a semi-spherical shape.